The present invention relates to an N-vinylformamide copolymer as the starting material for the production of a hydrophobic and high-molecular weight vinylamine copolymer obtained by modifying formyl groups in the N-vinylformamide copolymer, as well as a process for producing the same. More particularly, the present invention relates to a N-vinylformamide copolymer having the structural units represented by the following formulas (I) and (II): ##STR2## wherein R.sub.1 represents a hydrogen atom or a methyl group and R.sub.2 represents an alkyl group of 1 to 4 carbon atoms, in which the molar ratio between the structural units (I) and (II) is from 20:80 to 95:5, as well as a process for producing the N-vinylformamide copolymer.
A vinylamine copolymer obtained by modifying the formyl groups in N-vinylformamide copolymer according to the present invention has an excellent effect in the field of application of cationic polymers such as flocculating agent for the treatment of waste water, dehydrating agent for organic sludges, as well as drainage aid, retention aid and paper strength increasing agent in papermaking industry, etc.
It has been known for the process of producing a polyvinylamine by the Hofmann reaction of polyacrylamide and hydrolysis of poly-N-vinylamide. Among all, the method of hydrolyzing a homopolymer of N-vinylformamide is excellent method which is capable of synthesizing a polyvinylamine of a high-molecular weight with high stability. However, the resultant polymer has an extremely high hydrophilic property and only an insufficient effect in the case of using the polymer as a dehydrating flocculating. For providing the polyvinylamine with a hydrophobic property, there has been known a method of previously copolymerizing N-vinylformamide and ethylene and then hydrolyzing the resultant product, but it was difficult to solve the problem by the copolymer, since the copolymerizability between N-vinylformamide and ethylene is not satisfactory and, in addition, it is difficult to obtain a copolymer of high molecular weight.
In order to overcome the foregoing drawbacks, the present inventors have made an earnest study and, as a result, it has been found that a polyvinylamine copolymer obtained by modifying the formyl groups in the N-vinylformamide copolymer having the structural units represented by the following formulas (I) and (II): ##STR3## wherein R.sub.1 represents a hydrogen atom or a methyl group and R.sub.2 represents an alkyl group of 1 to 4 carbon atoms, in which the molar ratio between the structural units (I) and (II) is from 20:80 to 95:5 is a hydrophobic and high molecular weight polymer, and exhibits an excellent effect as a flocculating agent for use in the treatment of waste water and a paper strength increasing agent in papermaking industry, and based on the finding, the present invention has been attained.
The object of the present invention is to provide an N-vinylformamide copolymer capable of forming a high-molecular weight vinylamine copolymer having a hydrophobic property through a modifying reaction. The foregoing object of the present invention can be attained by an N-vinylformamide copolymer having the structural units represented by the formulas (I) and (II): ##STR4## wherein R.sub.1 represents a hydrogen atom or a methyl group and R.sub.2 represents an alkyl group of 1 to 4 carbon atoms, in which the molar ratio between the structural units (I) and (II) is from 20:80 to 95:5.